1. Field of the Invention
This invention relates to a polymer phase plate type liquid crystal device having a layer of phase film for optical compensation.
2. Prior Art
As known twisted nematic (TN) type liquid crystal devices have disadvantages of limited viewing angle and incompatibility with multiplexing drive, there has been proposed a super-twisted nematie (STN) type liquid crystal device to overcome such problems.
Since the color of the display system of a STN type liquid crystal device has a yellowy or bluish tint, efforts have been paid to produce a black and white display system by modifying a STN type crystal device.
An achievement of such efforts is a two-layered type device. A two-layered type device is formed by combining a liquid crystal cell for display and one having an inverse twist angle for optical compensation.
While a two-layered liquid crystal device possesses excellent display characteristics, its manufacturing cost can become prohibitive because of a long process line required and a poor yield rate of production of liquid crystal cells.
With a view to overcoming these problems, there has been proposed a polymer phase plate type device that utilizes, in place of a cell for optical compensation, a phase film having optical properties which are reverse of those of the liquid crystal cell to be used for display.
However, a polymer phase plate type device is accompanied by a problem of residual background color that makes it less favorable in terms of black and white display as comprared with a two-layered type device.
It is therefore an object of the invention to solve the problem of residual background color of an existing STN type liquid crystal device.